The present invention is related to integrated circuits. More specifically, the present invention can be applied to devices used controlling power supply. According to various embodiments, the present invention provides various power control schemes to improve system stability and performance. Merely by way of example, the present invention can be used in switch mode power conversion system including power-on reset and under voltage lockout circuits. It is to be appreciated that the present invention has a broad range of applications.
Power converters are widely used in various applications, such as providing power to portable consumer electronics. The power converters can convert electric power from one form to another form. As an example, the electric power is transformed from alternate current (AC) to direct current (DC), from DC to AC, from AC to AC, or from DC to DC. Additionally, the power converters can convert electric power from one voltage level to another voltage level. By converting electrical power to desired form and/or voltage, various devices can be properly powered.
In the past various types of power converters have been developed. For example, linear regulators have traditionally been used for power converters. A linear regulator is a voltage regulator based on an active device (such as a bipolar junction transistor, field effect transistor or vacuum tube) operating in its “linear region” or passive devices like zener diodes operated in their breakdown region. The regulating device is made to act like a variable resistor. While linear regulators have been used for many years, their power efficiency is often inadequate for portable electronics. For example, due to low power efficiency, linear regulators often waste large amount of energy and generate excessive heat for portable devices.
With the advent of integrated circuits, switched-mode power supply has been invented and utilized for various applications. Switch mode power supplies are typically implemented with a switching regulator, which is an internal control circuit that switches the load current rapidly on and off in order to stabilize the output voltage. For certain applications, switch-mode power supply uses pulse-width-modulated (PWM) or pulse-frequency-modulated (PFM) mechanism. These mechanisms are usually implemented with a switch-mode-controller including various protection components.
Typically, various types of power supplies are controlled by power-on reset (POR) and under voltage lockout (UVLO) circuits. For example, POR/UVLO circuits are used to hold the electronic systems in a “reset” mode during power on and off transitions. In addition, POR and UVLO circuits are sometimes used when the power supply voltage, which typically ranges from several volts to several tens of volts, is in an invalid state.
When an integrated circuit initializes (e.g., when powering up), the process usually starts with the supply voltage of the integrated circuit being switched on. During this process, the supply voltage will rise from zero to an operational supply voltage within a certain amount source impedance or source current. Before the operational supply voltage is reached, the integrated circuit is unable to properly function. Typically, the integrated circuit at this voltage is in an undefined and/or invalid state. For example, when the integrated circuit is at an undefined state, the integrated circuit should not operate; operating in an undefined state could potentially cause damages to the integrated circuit.
As explained above, it is thus desirable to prevent the integrated circuit from operating when it is in an undefined and/or invalid state (e.g., due to insufficient supply voltage). To disable integrated circuit form operating in an undefined state, the integrated circuit is usually put in to a reset mode, which can be accomplished by an UVLO circuit.
In addition to preventing the integrated circuit from operating when it is in an undefined and/or invalid state, it is often desirable to assure that various components of the integrated circuit are in a properly initialized before the integrated circuit starts fully operating. Usually, a POR/UVLO circuit is used to monitor voltages at various nodes of the integrated circuits to determine whether various components are properly initialized (e.g., whether these components reached their threshold voltage levels). Based on the monitored voltages, the POR/UVLO generates control signals that enable and/or disable various components and/or the integrated circuit.
Over the past, POR/UVLO circuits have widely used for various power systems. Conventional techniques for POR/UVLO power control have been developed to make POR/UVLO circuits more efficient and reliable. Unfortunately, these conventional techniques are often inadequate.
Therefore, it is desirable to have improved systems and methods for power control systems.